In his introduction Eyjólfur Emilsson explains that this book owes a good deal to a number of articles that he had previously published. But the book is all the better for that period of reflection and discussion, which has produced an extraordinarily stimulating analysis of what is probably the most central and engaging aspect of Plotinus' metaphysics. A useful introduction prepares us for the contents of the four chapters into which the book is divided. The first, on 'Emanation and Activity', examines the origin of Intellect as a product of the ultimate principle, the One. The core of the chapter is a detailed analysis of Plotinus' doctrine of 'double activity' which is his most philosophical exposition of the causal relationships obtaining between transcendent realities. The second chapter, 'The Genesis of Intellect', engages with the reasons why and how it is that the product of the One is an Intellect. New light is here thrown on the concepts of procession and return, the way in which the second 'Hypostasis' is a plurality and what sort of 'self-thinking' constitutes its cognitive activity. The third chapter, 'Intellect and Being', moves away from Intellect's relationship with the One to clarify the internal structure of Intellect on its own terms: the identity of thinker and object of thought, and how an object of thought is an intellect. The final chapter, 'Discursive and Non-discursive Thought', raises the question of the nature of the kind of non-discursive thought that Plotinus ascribes to Intellect and how this relates to the discursive thought, which he recognises as being the normal cognitive activity of human beings. If this book is primarily about Intellect as a universal principle, this last chapter reminds us that Plotinus also thinks that each individual is endowed with an intellect which in some way brings him into contact with the universal Intellect. Thus, what is said about Intellect is also of direct relevance to the human individual, and Plotinus' analysis of the cognitive activity of the divine Intellect is both illuminated by and illuminates our understanding of our own mental activities. It is worth noting at this point Emilsson's advance apology for his general approach, which, he feels, may be perceived as falling between the two stools of modern philosophical analysis and the traditional philological approach to the history of philosophy. I found his approach an admirable and judicious combination of both methods. He always keeps close to the text and fully appreciates the intellectual context of Plotinus' concepts and style of philosophising, whilst at the same time he can deepen our understanding of the text by posing questions inspired by modern philosophical concerns.

It is difficult to do justice to the abundance of interpretive ideas in this book. Thankfully there is a useful index of passages discussed, which will make it easier for the reader to use the volume whenever reading the Enneads. I will limit myself to pointing out some of the ideas which I found most engaging. Emilsson rightly identifies the theory of 'double activity' as of central importance for Plotinus' metaphysics. With this theory Plotinus accounts for the production of a lower reality as an activity derived from its prior as a by-product of the higher reality's own innate activity which constitutes its essence (as heat is produced from fire). The theory raises a number of issues which E. explores with clarity. For example, are there really two activities or one, if you push the consequences of Plotinus' metaphor of the derived activity as a 'trace' as in the case of walking and leaving a footprint? Does Plotinus contradict himself when referring sometimes to the inner activity of One and elsewhere denying that the One has an activity? Such 'contradictions' are, argues E., more apparent than real; what Plotinus is denying is that the One has an activity whose cause lies outside itself, whilst as the dunamis pantôn it is the active cause of everything. After reviewing the evidence for the origin of the theory (Aristotle and primarily Plato are mentioned here), E. concludes that the theory is largely Plotinus' own. The external activity of the One is not quite yet an Intellect but what E. calls an inchoate Intellect, which to become fully formed Intellect must 'return' to contemplate the One. E. probes relentlessly the reason why it should 'return' and is, I think, right to suggest that it is already endowed with an indeterminate desire (p.74). His analysis, always supported by the text, is helpful in dispelling the impression we may easily have of a rather abstract, mechanical and even gratuitous metaphysical construct. Also clear and helpful is E.'s distinction within Intellect of two kinds of plurality: the duality of thinker and object of thought, and the plurality of objects of thought. He neatly demonstrates that there is a connection between the two kinds of 'otherness' (which constitutes difference and, therefore, plurality) and that for Plotinus these are in the end two aspects of the same plurality. This becomes clearer with his examination of the nature of the reflexive thinking of Intellect (110f). In addition E. argues that although Plotinus owes much, as previous interpreters have pointed out, to Aristotle, his Intellect is, unlike that of Aristotle, a fully reflexive self-thinker in the sense of thinking of itself as an I. His analysis of self-thinking here is an advance on previous good work on the topic.

He also sees that the strong contrast in V.5.1. of sense perception and intellectual vision presents a problem. Not only is intellection often described in terms of vision but V.5.1 appears to suggest that in sense perception we see only an image of the external object, whereas elsewhere Plotinus is not so disparaging of sense perception as to adopt what is virtually an antirealist position. E. is here revisiting a point raised in his book on sense perception in Plotinus (Plotinus on Sense Perception, Cambridge 1988) and one which has excited some controversy. His interpretation here is more nuanced and attractive. He argues that V.5.1. is deliberately more extreme than usual in formulation in order to make a strong point about the uniqueness of Intellect's grasp of its object. But far from contradicting his normal view about the status of the object in sense perception, it can be shown that V.5.1 complements what he says elsewhere. To demonstrate this, E. attractively applies the double activity theory to Plotinus' theory of sense perception. The senses, in perceiving what in the external world is the form (external activity of the logos) in matter, become aware, in a sensible mode, of the transcendent logos (internal activity), which is the direct cause of the immanent form. To the extent that the senses have this, admittedly limited, access to the logos they grasp the cause/essence of the perceived object. In the case of Intellect the grasp of essence is at its own level and is therefore a clearer vision. Even if it might be difficult to accept all of E.'s interpretation here, certainly this method of interpretation of Plotinus by Plotinus adds richness to the debate and sharpens our alertness and sensitivity in reading the text.

Another area of difficulty is found in Plotinus' apparently contradictory statements about the priority of Being to Thought/ Thought to Being. But this is readily dispelled once we understand that they are co-equal. Can we say that even the inchoate intellect is prior to Being? Not even that, since it is no less potential intellect than Being is potential Being. This conclusions leads to a sensible discussion of the meaning of 'potentiality' in the intelligible world.

In the final chapter on discursive and non-discursive thought, E. concerns himself primarily with trying to determine what Plotinus means by non-discursive thought rather than with the more general question of whether there can be such a thing. One of the key issues in recent debates concerns the prepositional nature of Intellect. E. here steers course through the disagreement of Lloyd, who denies complexity and therefore propositionality, and Sorabji, who accepts complexity in Intellect and therefore its propositional nature. (Sorabji, however, distinguishes this propositionality from the propositional nature of discursive thought, which is inferential, whereas Intellect deals in non-inferential statements or definitions of Forms.) E. argues that each of these views is flawed in that they equate complexity with discursivity. Yet there is no doubt that Intellect is complex. Equally, Plotinus appears to deny in many passages that it entertains propositions. But, E. argues, when Plotinus refers to protaseis, axiomata or even lekta (the latter only in V.5.1) he may have understood them as representational, and so denying 'the representational nature of sentences rather than propositional structure as such' (p.191). This is a useful discussion and a good example of how an application of distinctions, which, E. carefully warns us, were probably not available to Plotinus himself, may help us to navigate problems of interpretation for which our own non-Plotinian concepts are at least partly responsible.

This is a book that has as much to teach us about methods of interpretation as it does to help us to understand some essential issues in the Enneads. Not the least contribution to the utility and readability of the volume is the generous citation of all passages discussed together with the Greek text in the footnotes. This format makes it easy to use as a monograph, but its index of passages will also provide those reading Plotinus ready access to a wealth of intelligent and stimulating interpretations of many difficult sections of the Enneads.